Put two property listings side by side. Both carry the word “auction”. Both show a guide price, a countdown and a button to register and bid.
One is being sold by traditional auction. If your bid is accepted under the auction conditions, you have normally entered into the contract to buy the property there and then, with completion following on the timetable set out in the legal pack. The other is being sold through the Modern Method of Auction. If you win that auction, you have not normally exchanged contracts to buy the property. Instead, you enter into a reservation agreement, pay a potentially substantial reservation fee and get a defined period in which the transaction is expected to reach exchange and completion.
Those are very different commitments hiding behind the same word.
That difference matters because auction misunderstandings are generating a disproportionate number of complaints. In its May 2026 report on property auctions, The Property Ombudsman said auctions accounted for just over 2% of UK residential sales in 2025 but 9% of residential sales complaints. Buyers and prospective buyers brought 68% of auction-related residential sales complaints, with Modern Method arrangements, reservation fees, deadlines and withdrawal consequences among the recurring areas of confusion.
This article is about that central question: when do the buyer and seller become committed, what have they committed to, and how expensive can changing course become? The answer depends on the particular auction conditions, reservation agreement and lot documents. “Traditional auction” and “Modern Method” describe broad structures, not one universal contract.
The article principally describes practice in England and Wales. Scotland and Northern Ireland have different conveyancing systems, and auction arrangements there should be checked on their own terms.
The method matters more than whether the auction is online
A traditional auction — sometimes described as an unconditional auction — can take place in a room, online, by telephone or through a live-streamed event. The important feature is what happens when the successful bid is accepted. Under the conventional unconditional model, that point normally creates the binding contract for the property.
Modern Method of Auction, commonly shortened to MMoA and often described as a conditional auction, separates the auction result from exchange of contracts. The successful bidder normally enters into a reservation agreement, pays a reservation fee or reservation deposit and receives a defined period in which the conveyancing and finance can progress before contracts for the property are exchanged.
A timed online auction can therefore be traditional or conditional. The screen format tells you very little about the legal structure.
The same caution applies to the guide price. It is not a valuation and it is not a promise about what the property will sell for. Current ASA/CAP guidance on auction guide prices describes the guide as an indication of the seller’s minimum expectation, while the reserve is the minimum price below which the auctioneer is not authorised to sell. Competitive bidding can take the final price well above either figure.
A guide price is useful for deciding whether a property deserves further investigation; it is a poor substitute for a buying budget. Buyers should also look for non-optional fees shown alongside or clearly signposted from the guide price, because a property that appears attractive at £180,000 can become a very different proposition once buyer premiums, reservation charges or other compulsory costs are included.
Before bidding, the useful question is therefore not “is this an online auction?” or even “what is the guide price?”. It is what happens legally and financially if you are the successful bidder, and what the property will cost you in total if you are.
Traditional auction: the due diligence happens before the bid
In a conventional unconditional auction, a successful bid normally creates the property contract immediately. That reverses much of the sequence familiar from an ordinary private-treaty purchase, where a buyer can agree a price and then investigate the title, arrange a survey and secure the mortgage before exchange.
Traditional auction pushes much of that work in front of the bid. There is normally no later “subject to survey” or “subject to mortgage” stage in which a buyer can reconsider without contractual consequences.
Where an auctioneer uses the current RICS auctioneering standard and Common Auction Conditions, the default deposit is the greater of 10% of the purchase price or any minimum deposit stated in the conditions. Where the special conditions do not specify another completion date, the default is 20 business days after the contract date.
Those are defaults, not promises. The special conditions for an individual lot can alter the deposit, completion date, buyer charges and other obligations, and those lot-specific terms are ultimately what the buyer is accepting.
The same applies to the legal pack. Under the RICS structure, a buyer can be treated as having knowledge of information made available before the auction and may have little opportunity to object afterwards to something they could have investigated beforehand. Traditional auction therefore offers contractual certainty quickly, but it asks buyers to do the expensive thinking earlier.
That also extends beyond title and finance. Under the RICS defaults, unless the special conditions provide otherwise, the seller has no obligation to insure the property after the contract date and the buyer bears the risk of loss or damage. A successful bidder can therefore become contractually responsible for a property weeks before receiving the keys and needs to understand what insurance is required from the auction date.
The final check should happen immediately before bidding, not two days beforehand. RICS advises buyers to stay in contact with the auction firm because information can change before a lot is offered. Recheck the legal pack, special conditions and any auction addendum rather than assuming the version you downloaded earlier in the week is still the final one.
This is why finance, legal review, property condition and the ability to complete are pre-bid questions in a traditional auction, not problems to solve after you have won.
Modern Method: the reservation is a real commitment even before exchange
Modern Method works differently, but describing the buyer as “not legally committed until exchange” is too simplistic.
The buyer is normally not yet bound by the property purchase contract when the auction ends, but they will usually enter into a reservation agreement straight away. That agreement can itself impose contractual obligations concerning exclusivity, fees, deadlines and withdrawal. Exchange of contracts for the property comes later.
There are therefore two different commitments: first to the reservation arrangement, and later to the purchase itself.
A 56-day structure is common in Modern Method sales and can give a mortgage-backed buyer substantially more time than a traditional auction, but it is not a statutory timetable. Individual providers can structure the deadline differently, including when the clock starts, so the reservation agreement matters more than the headline promise of “56 days”.
The reservation fee is where much of the practical risk sits. It is important to distinguish a reservation fee from a reservation deposit: a fee is commonly an additional cost on top of the winning bid and does not reduce the balance of the purchase price, while a reservation deposit can be structured so that it contributes towards the price. The paperwork should make clear which one is being charged and what happens to it if the transaction fails.
A buyer should not assume that a bad survey, a disappointing mortgage valuation or a lender taking too long automatically produces a refund. Nor should they assume the seller withdrawing has the same consequence under every provider’s terms. TPO’s 2026 report specifically identifies refund triggers, seller withdrawal, failed finance and reservation extensions as areas that need to be explained clearly before the buyer pays.
The scale of the fee can make this more than a technical distinction. If a particular lot carries a 4.5% reservation fee, a £200,000 winning bid creates a £9,000 additional charge before the buyer has paid for conveyancing, a survey, mortgage costs or the move itself.
Whatever the auction method, the maximum bid should therefore be based on the all-in acquisition cost rather than the headline bid alone. Reservation fees, buyer premiums, administration charges and costs transferred to the purchaser through the special conditions can materially alter what appears to be a bargain. RICS guidance for auctioneers specifically recognises that sellers can require buyers to contribute to items such as the seller’s legal or auction costs and that those additional payments should be disclosed so buyers can calculate the real cost of purchase.
Some of those charges can also affect transaction tax. In England, HMRC’s guidance on auction-house fees gives the example of a buyer paying the seller’s auction-house fee, with that payment forming part of the chargeable consideration for Stamp Duty Land Tax. It does not mean every registration, administration or reservation charge is automatically included: the treatment depends on what the payment is actually for and how it relates to acquiring the property.
Wales uses Land Transaction Tax rather than SDLT. The Welsh Revenue Authority’s guidance on chargeable consideration likewise explains that seller costs paid by the buyer as part of the transaction, including auction-house commission, can form part of the consideration for LTT.
For either tax, the sensible time to establish the treatment is before bidding, when the buyer can still decide what the lot is genuinely worth to them.
Modern Method therefore gives a buyer something traditional auction usually does not: more time between winning and exchange to progress mortgage and conveyancing work. What it does not necessarily provide is the freedom of an ordinary accepted offer. If legal enquiries, the survey or finance create a problem, money may already be at risk. An extension can sometimes be agreed, but it should be confirmed in writing rather than assumed.
Sellers are committed differently too
The distinction between the two methods matters just as much to the seller.
In a traditional unconditional auction, buyer and seller normally become bound to the property transaction at the same point. Once the reserve has been met and the qualifying bid accepted, the seller cannot simply decide afterwards that the price was disappointing and continue marketing the property. Before the lot is sold, withdrawal may still be possible, but the auctioneer’s terms can determine what fees or expenses remain payable.
Modern Method is more layered. During the reservation period there may not yet be an exchanged contract for the property sale, but the seller may already be bound by separate terms with the auction provider or estate agent. Those terms can restrict marketing elsewhere, create exclusivity or impose costs if the seller withdraws.
That is why neither side should read “contracts haven’t exchanged” as meaning “nothing is binding”. The real question is which agreement has already taken effect and what it says happens if either side changes their mind.
For sellers there is also an economic point worth recognising. An arrangement advertised as having little or no seller fee is not necessarily cost-free in a wider sense if a substantial buyer-paid reservation fee changes what bidders can afford, or are prepared, to bid for the property itself.
Traditional and Modern Method side by side
The comparison below describes common structures rather than universal terms. The paperwork for the individual lot can alter any of them.
| Traditional / unconditional auction | Modern Method / conditional auction | |
|---|---|---|
| Property contract | Normally binding when the winning bid is accepted | Normally exchanged later within the reservation process |
| Immediate commitment | Buyer and seller are normally committed to the property sale | Parties may already be contractually committed to reservation or agency terms even though the property contract has not exchanged |
| Money usually required on winning | Deposit, commonly 10% under RICS defaults, plus disclosed buyer charges | Reservation fee or reservation deposit, plus other disclosed charges |
| Does the first payment reduce the price? | Deposit does; buyer premiums or administration charges generally do not | Depends: reservation fee commonly does not; reservation deposit may |
| Typical timing | Usually short; RICS default is 20 business days where special conditions do not specify otherwise | Longer fixed reservation periods are common; 56-day structures are widely used, but terms vary |
| Mortgage purchase | Possible, but finance must meet the short contractual timetable | More time is normally available for mortgage and legal work before exchange |
| Buyer decides not to proceed | Potential deposit loss and further liability for breach | Reservation payment may be lost; other consequences depend on the agreement |
| Seller decides not to proceed | Seller may be in breach of the property contract | Consequences depend on reservation, agency and auction-provider terms |
The central distinction is not simply that one method is fast and the other slower. Traditional auction normally commits the parties to the property sale itself immediately; Modern Method normally creates a reservation commitment first, with the binding property contract following later.
An offer before the auction does not automatically become an ordinary sale
Many auction properties invite offers before the scheduled auction or bidding deadline. That can work for both sides: the buyer removes the uncertainty of competition and the seller may secure an acceptable figure without waiting.
The mistake is assuming an accepted pre-auction offer automatically turns the transaction into an ordinary estate-agency sale.
A seller using a traditional auction may accept an early offer on the same unconditional terms intended for the auction, which can mean an accelerated exchange and the same need for legal review, finance and deposit funds to be ready. A Modern Method provider may treat the accepted offer as triggering the same reservation agreement and buyer fee that would have followed a winning bid. In other cases, the parties may expressly agree different terms.
The words “pre-auction offer” therefore tell the buyer less than the answer to one practical question: if the seller accepts this figure today, exactly what agreement am I expected to sign and exactly what money becomes payable?
Neither method is automatically better
Traditional and Modern Method auctions transfer risk differently rather than simply offering a better and worse version of the same sale.
Traditional auction concentrates much of the buyer’s risk before and at the bidding point. The legal pack needs to be understood, the property’s condition investigated, the all-in cost calculated and finance capable of meeting the timetable. In return, the seller normally receives strong contractual certainty as soon as the successful bid is accepted.
Modern Method gives the buyer longer to progress the mortgage and legal work before exchange, which can make auction-style selling accessible to a wider group of purchasers. The trade-off is a reservation structure in which substantial money can already be at risk even though the purchase contract itself has not yet been exchanged.
A buyer who understands that difference may decide either method suits them perfectly well. The expensive problems tend to begin when somebody enters one transaction believing they are in the other.
Before bidding — or before a seller agrees to list through either method — four questions should have clear answers:
- What agreement becomes binding first?
- At what point am I bound to the property sale itself?
- What money will I have paid or become liable for by then?
- What can I lose if the transaction does not proceed?
If those answers are not clear, the word “auction” is not enough information to make the decision.
Important: This article provides general information about residential property auctions and is not legal, tax, mortgage or financial advice for a particular transaction. Auction conditions, reservation agreements, fees, completion periods and remedies vary between providers and individual lots, and property law and transaction taxes differ across UK jurisdictions. Before making a binding bid or paying a reservation fee, have the relevant legal documents reviewed by an appropriately qualified conveyancer and make sure you understand the consequences if the purchase or sale does not complete.
